The present invention relates generally to purification of proteinaceous substances and more particularly to isolation of plasma albumin by means of ion exchange chromatographic procedures.
Among the more abundant and therapeutically significant proteinaceous materials in blood plasma is albumin. This material is present, for example, in human blood plasma at a concentration of approximately 35 to 55 grams per liter. As is the case with other biological fluids, blood plasma is most commonly fractionated--and albumin is most commonly isolated from among 30 or more other plasma proteins--by methods based on differential solubility of component proteins in aqueous and aqueous-organic solvent systems. The predominant plasma fractionation procedure presently employed for isolation of albumin from plasma is the "Cohn" cold ethanol procedure [Cohn, et al., J.M. Chem. Soc., 68 pp. 459-475 (1946); see, also, U.S. Pat. No. 2,710,294]. Briefly put, the Cohn process is predicated on selective solubility of proteins under varying conditions of ethanol solvent concentration, protein concentration, temperature, ionic strength and pH. By selective precipitation of proteins from successive supernatants, albumin is eventually isolated in a commercially desirable purified form. See, generally, Kirk-Othmer, "Encyclopedia of Chemical Technology", Vol. 3, pp. 576-600. It is unfortunately the case that successive precipitations in the cold alcohol process will result not only in loss of plasma albumin (and diminution of final yields) but will result also in some degree of destruction of functional or structural characteristics of albumin. Thus, each successive precipitation and resuspension, may enhance the purity, but may also affect the native character of the albumin.
In response to chronic low yield problems in cold alcohol fractionation procedures, the art has developed alternative fractionation processes involving ion exchange chromatography. Solid-liquid column chromatography has classically been a versatile and highly beneficial technique for a fractionation and purification of proteins owing to the high degree of selectivity of ion "exchangers" available. This selectivity, when applied to plasma fractionations directed toward isolation of albumin, has resulted in advantages over prior alcohol treatment processes in terms of both increased purity and yield of albumin. There have been reports, for example, of overall albumin yields from starting plasma on the order of 95% or better, as well as reports of immunoelectrophoretically verified purity for albumin products in excess of 96%. See, e.g., Curling, et al., Vox Sanguinis, 33, No. 2, pp. 97-107 (1977).
While the production of such "chromatographically pure" albumin in high yields constitutes an advance over prior art isolations, the chromatographic procedures reported have not been shown to be significantly less destructive of the native characteristics of the albumin than are the cold alcohol fractionation procedures. It is noteworthy, for example, that known ion exchange chromatographic methods for purification of albumin often involve multiple precipitation and resuspension steps similar to those extant in the cold alcohol fractionation processes and further involve multiple desorbtions of the albumin from the ion exchanger materials. Each such manipulation increases the potential for adverse changes in the native character of the albumin molecules.
There exists, therefore, an ongoing need for new procedures which will efficiently isolate purified albumin from plasma while minimizing potential alterations in the native structure or character of the albumin or other plasma components. A reduction in handling or manipulation, with or without greater yield has obvious advantages in commercial applications as well.